International civil aviation organization

Router Fundamentals

All routers and routing protocols discussed within this document are ICAO Doc. 9705 Boundary Intermediate Systems (BISs). Using the IPS terminology, all routers discussed within this document are “Border Gateway (BG)” routers that communicate between Autonomous Systems.

1. BIS and Border Gateway Systems

• 
  Backbone BISs/BGs (BBISs/BGs), and
  
• 
  End BISs/BGs (EBISs/EBGs)
  

1. Backbone BIS/BG

A BBIS/BBG is a router that primarily routes PDUs between routing domains or ASs. These routers are typically higher performance routers that aid in the efficient flow of data between domains/ASs. BBIS/BBG may have End-Systems connected to them, but they are often limited to router-to-router connections.

2. End BIS

End BISs/BGs are connected to one or more BBISs/BBGs and provide routing services to a single routing domain/AS. Further End BISs do not act as a transit router for passing PDUs between other routing domains/AS.

3. CAR/SAM AMHS Ground-to-Ground Routing Architecture

The CAR/SAM AMHS routing architecture is to the largest degree possible independent of the protocol family (ATN/OSI or IPS) or specific routing protocols. The CAR/SAM routing architecture is based upon several concepts:

1. 
   From the IPv6 addressing specification, “routing-domains” are defined as specific address prefix lengths.
   
2. 
   Based on the definition of “routing-domain” prefix definitions, each routing domain can be considered an Autonomous System (AS).
   
3. 
   States will make their own implementation and transition decisions.
   

The routing architecture can be divided into several distinct parts:

• 
  the definition of the backbone routing structure for passing information between routing domains within the Region;
  
• 
  the definition of the routing structure between routing domains not on the backbone;
  
• 
  the definition of the routing structure for use in end-routing domains; and
  
• 
  the definition of the routing structure for passing information from this Region to other Regions.
  

The first component is the definition of the backbone routing structure that supports the exchange of data within the Region. This part defines the interconnection of the major communication facilities in the Region and how they cooperate to link all of the systems in the Region.

1. CAR/SAM Backbone

The definition of a Regional Backbone is based upon the efficiencies that may be realized by concentrating AMHS traffic at major communication centers and using the economy of scale in passing this information between major communication centers.

2. Inter-Regional Backbone

The second component of the CAR/SAM Routing architecture is the definition and potential location of Inter-Regional Backbone Routers. The manner in which this architecture was developed was to ensure that the use of the existing communication infrastructure is possible to the greatest degree. The use of the existing communication infrastructure should reduce the overall cost of transitioning to the AMHS.

3. End BISs

It is assumed that naming and addressing (and routing domain definition) will be done on a Regional basis. Further that for areas within the Region that may utilize an End BIS service more than one State, the naming structure will be based on the Regional IPv6 addressing plan as defined.

4. AMHS IPS-Based Ground-to-Ground Routing

The Region has already made the decision to provide ATN AMHS services over an appropriately defined TCP/IPv6 communication infrastructure. The following sections describe the implementation of the Regional routing architecture within the scope of IPv6 routing.

1. Internet Protocol Suite Routing Protocols

Within the scope of the routing of IPv6 traffic there are defined several different protocols. For the purposes of intra-domain routing typical protocols are RIPv2 and OSPF. For the purposes of inter-domain routing, BGP-4 is the most prevalent.

3. BGP-4

The Border Gateway Protocol (BGP) is the routing protocol used to exchange routing information across the Internet. It makes it possible for ISPs to connect to each other and for end-users to connect to more than one ISP. BGP is the only protocol that is designed to deal with a network of the Internet's size, and the only protocol that can deal well with having multiple connections to unrelated routing domains.

1. BGP-4 Requirements

In order to use BGP-4 for routing within the Region, each BGP-4 router must meet the following minimum requirements.

Each routing-domain/AS must obtain an AS number.
Note: The method of obtaining an AS number is within the scope of the IPv6 Address document.
Each BGP-4 router must have an appropriate MD-5 certificate/password assigned and managed.
Note: The procedures for generating, managing, distributing MD-5 certificates are TBD.

2. Policy Based Routing

   1. Types of Policy

The BGP-4 decision process (and thus AMHS routing policy) is conditioned by three types of policy concerns.

• 
  Route Aggregation policies permit BGP-4 routers to reduce the amount of routing information propagated.
  

• 
  Route Preference policies determine which routes will be installed in the Forwarding Information Base. Route preference policies thus determine which path a router will select to forward IPv6 pdus on.
  

• 
  Route Distribution policies determine which routes a BGP-4 router will advertise to other BGP-4 routers. Route distribution policies are a key aspect of a routing-domain’s/AS’s transit policy in that they determine which routes will be permitted in a domain. A BGP-4 router will not propagate a route, which it does not wish to support. By selective advertisement of routing information BGP-4 routers control the use of their own resources since other routers cannot choose a route they do not know about.
  

4. General Framework for AMHS BGP-4 Routing Policy

   1. Routing Policy Goal for BGP-4 routers

• 
  CAR/SAM Regional BGP-4 routers will provide global shortest path connectivity with a minimal exchange of routing information.
  

• 
  CAR/SAM Regional BGP-4 routers will not exchange any routing information for any IPv6 address not defined as an “ICAO State or Organization” address. (No connectivity to global internet routers or hosts.)
  

• 
  CAR/SAM Regional BGP-4 routers will not connect to any router not owned or operated by a State or Organization. (No connectivity to global internet routers or hosts.)
  

2. Network Organization for Routing to Ground Systems

As presented in earlier sections, the AMHS ground infrastructure may be partitioned into various levels of organization. Routing domains at the highest level are associated with an ICAO region. The CAR/SAM IPv6 Addressing Plan should provide an IPv6 address structure that partitions the address space to include NLRI prefixes that vary according to the level of organization. Within the CAR/SAM Region, routing domains are next associated with a particular state or organization. Note that the regional addressing plan should specify a field within the IPv6 address that can be uniquely assigned to the state or organization. Finally, within a particular state or organization there may be multiple local routing domains (which may or may not be visible outside of the particular state or organization).

3. Policy for BGP-4 Routes to AMHS Systems

The policy requirements for BGP-4 routers in the CAR/SAM Region for routes to AMHS systems are specified in this section. The following sub-sections specify the policies according to the classification:

1. 
   the general policy for routes to ground systems; the policy for inter-regional routes;
   

2. 
   the policy for intra-regional routes; and
   

3. 
   the policy for local routes.
   

1. General Policy

1. 
   If a backbone router receives multiple routes to an aggregate or specific destination, the route with the shortest path ([i.e., shortest list of AS)] shall be selected.
   
2. 
   All BGP-4 routers in the Region shall authenticate the identity of peer ATN routers.
   

2. Policy for Inter-Regional Aggregate Routes To Ground Systems

Inter-Regional route aggregation is only possible where a bi-lateral agreement exists between the two States to operate BGP-4 routers.

3. Policy for Intra-Regional Aggregate Routes to Ground Systems

Intra-regional route aggregation permits advertisement of a single aggregate route which identifies all systems in a particular State or Organization of an ICAO region. Aggregation at an intra-regional level refers to aggregating NLRI fields in the IPv6 address prefix up through the complete [TBD] field.

1. Intra-Regional Route Aggregation Policies

1. 
   Backbone routers with intra-regional connectivity shall be configured with aggregate routes to AMHS system at an intra-regional level.
   

2. Intra-Regional Route Preference Policies

1. Intra-Regional Route Distribution Policies

2. 
   Backbone routers with intra-regional connectivity shall distribute intra-regional aggregate routes to adjacent AMHS BGP-4 routers.
   
3. 
   Routers with local connectivity shall distribute intra-regional aggregate routes to adjacent AMHS BGP-4 routers.
   

4. Policy for Aggregate Routes to Ground Systems for Distinct Routing Domains within a State/ Organization

Distinct Routing Domain-level aggregation permits advertisement of a single aggregate route which identifies all systems in a specific routing domain of a particular State or Organization of an ICAO region. Aggregation at this level refers to aggregating NLRI fields to an agreed IPv6 address prefix [TBD]. AMHS BGP-4 routers connecting to adjacent routers within a particular state or organization, i.e., with intra-state or intra-organizational connectivity, are said to have “local” connectivity.

1. Distinct Routing Domain Route Aggregation Policies

2. Distinct Routing Domain Route Preference Policies

3. Distinct Routing Domain Route Distribution Policies

4. Local State/Organizational Routing Policies

Honduras-Jamaica-USA (Alternative Routing 1)

Honduras-Cayman Island-USA (Alternative routing 2)
Jamaica-USA (Primary routing)

Jamaica-Honduras-USA (Alternative routing 1)

Venezuela-USA (Primary routing)

Venezuela-Trinidad-USA (Alternative routing 1)

Venezuela-Peru-USA (Alternative routing 2)

Venezuela-USA-Trinidad (Alternative routing 1)

Venezuela-Peru-Brazil (Alternative routing 1)

Venezuela-USA-Brazil (Alternative routing 2)
Venezuela-Peru (Primary routing)

Venezuela-Brazil-Peru (Alternative routing 1)

Venezuela-USA-Peru (Alternative routing 2)
Trinidad-USA (Primary routing)

Trinidad-Antigua-USA (Alternative routing 1)

Trinidad-Venezuela-USA (Alternative routing 2)
Colombia-Peru (Primary routing)

Colombia-Venezuela-Peru (Alternative routing 1)

Colombia-Ecuador-Peru (Alternative routing 2)
Peru-Brazil (Primary routing)

Peru-Venezuela-Brazil (Alternative routing 1)

Peru-USA-Brazil (Alternative routing 2)
Peru-Venezuela (Primary routing)

Peru-USA-Venezuela (Alternative routing 1)

Peru-Brazil-Venezuela (Alternative routing 2)
Argentina-Peru (Primary routing)

Argentina-Chile-Peru (Alternative routing 1)

Argentina-Paraguay-Peru (Alternative routing 2)
Brazil-Peru (Primary routing)

Brazil-USA-Peru (Alternative routing 1)

Brazil-USA (Primary routing)